Wow ~ sorry to hear of your damage. Unfortunately there aren't a lot of WeeWinds out there...even on this side of the pond, so a 'spare' would not be easy to come by! Your best bet would be to try & rescreen it...but in the door within a door models, the door itself may have to be disassembled in order to replace it. I'm not exactly sure what would be involved to do so but we may be tackling a similar project in our '56.
If it just needs to be straightened out, possibly a roller of some sort on the opposite side than your buddies head. I think they used aluminum screen back then and it might be able to be straightened...but then again if it is stretched, possibly not. Pics might help...but it could be hard to photograph.